Engine rotational speed control apparatus

Abstract

An engine rotational speed control apparatus is provide to prevent a degradation of fuel efficiency caused by an unnecessary increase of the rotational speed of an engine when a depression amount of an accelerator pedal is briefly increased and then immediately decreased. In particular, when the vehicle is accelerated, an optimum fuel efficiency operating point along an optimum fuel efficiency curve is not moved immediately to another optimum fuel efficiency operating point corresponding to a new target drive force. Instead, the target drive force is reached by increasing the engine load while increasing the engine rotational speed as little as possible, and thus using an operating point that does not lie on the optimum fuel efficiency curve.

1. An engine rotational speed control apparatus comprising:
 a fuel economy consumption operating point computing section configured to determine a fuel economy consumption operating point based on a combination of an engine rotational speed and an engine torque lying on a fuel economy consumption operation curve that achieves a requested engine output with a scheduled fuel economy consumption; 
 a rotational speed suppression operating point computing section configured to determine a rotational speed suppression operating point based on a combination of the engine rotational speed and the engine torque lying on a rotational speed suppressing operation curve that achieves the requested engine output with the engine rotational speed being lower than would be obtained using the fuel economy consumption operating point lying on the fuel economy consumption operation curve; 
 a requested engine output change detecting section configured to detect a change in the requested engine output; 
 a fuel amount comparing section configured to determine if a fuel efficiency degradation amount is larger than a rotational speed restoration fuel consumption amount upon the requested engine output change detecting section detecting that the requested engine output has increased to an increased requested engine output, with the fuel efficiency degradation fuel increase amount indicating an amount by which a fuel consumption amount that would result if the increased requested engine output was achieved using the rotational speed suppression operating point exceeds a fuel consumption amount that would result if the increased requested engine output was achieved using another fuel economy consumption operating point of the fuel economy consumption operation curve, and the rotational speed restoration fuel consumption amount indicating an amount of fuel that would be consumed by increasing the engine rotational speed to move the rotational speed suppression operating point from the rotational speed suppressing operation curve to the another fuel economy consumption operating point corresponding to the requested engine output; and 
 a continuously variable transmission control section configured to control the engine rotational speed by controlling the gear ratio of the continuously variable transmission such that the increased requested engine output is achieved using the rotational speed suppression operating point before the fuel amount comparing section determines that the fuel efficiency degradation fuel increase amount is larger than the rotational speed restoration fuel consumption amount, such that the increased requested engine output is achieved using the fuel economy consumption operating point after the fuel amount comparing section determines that the fuel efficiency degradation fuel increase amount is larger than the rotational speed restoration fuel consumption amount, and such that the requested engine output is achieved using the fuel economy consumption operating point when the requested engine output change detecting section detects that the requested engine output has decreased. 
 
     
     
       2. The engine rotational speed control apparatus as recited in  claim 1 , wherein
 the fuel economy consumption operation curve is a fuel efficiency operation curve made up of fuel efficiency operating points that are based on the engine rotational speed and the engine torque at which a given engine output is achieved with a minimum amount of fuel consumption. 
 
     
     
       3. The engine rotational speed control apparatus as recited in  claim 1 , wherein
 the fuel economy consumption operation curve is a fuel efficiency emphasized operating curve obtained by applying a smoothing processing to changes of the fuel economy consumption operating point while tracing a fuel efficiency operation curve made up of fuel efficiency operating points that are based on the engine rotational speed and the engine torque at which a given engine output is achieved with a minimum amount of fuel consumption. 
 
     
     
       4. The engine rotational speed control apparatus as recited in  claim 1 , wherein
 the rotational speed suppressing operation curve is set such that the engine rotational speed of the rotational speed suppression operating point is lower than the engine rotational speed of the fuel economy consumption operating point at which a given requested engine output is achieved by an engine rotational speed decrease amount at which the fuel efficiency degradation fuel increase amount of the rotational speed suppression operating point with respect to the fuel economy consumption operating point is substantially equal to an engine rotational speed recovery fuel consumption amount that indicates a fuel consumption amount required to increase the engine rotational speed so as to change from the rotational speed suppression operating point to the fuel economy consumption operating point. 
 
     
     
       5. The engine rotational speed control apparatus as recited in  claim 4 , wherein
 the continuously variable transmission control section includes a scheduled gear shifting pattern that is used in a gear shifting control of the continuously variable transmission such that the engine rotational speed of the fuel economy consumption operating point is set as a target engine rotational speed; 
 the fuel economy consumption operating point computing section is further configured to find the engine rotational speed of the fuel economy consumption operating point using the gear shifting pattern; and 
 the rotational speed suppression operating point computing section is configured to find the engine rotational speed of the rotational speed suppression operating point by subtracting the engine rotational speed decrease amount from the engine rotational speed of the fuel economy consumption operating point that was found using the gear shifting pattern. 
 
     
     
       6. The engine rotational speed control apparatus as recited in  claim 5 , wherein
 the fuel amount comparing section is further configured to select the larger of the target engine rotational speed that is currently used and the engine rotational speed of the rotational speed suppression operating point as a new target engine rotational speed when the requested engine output change detecting section detects that the requested engine output has increased, and to select the smaller of the target engine rotational speed that is currently used and the engine rotational speed of the fuel economy consumption operating point as the new target engine rotational speed when the requested engine output change detecting section detects that the requested engine output has decreased; and 
 the continuously variable transmission control section is further configured to control the continuously variable transmission to the new target engine rotational speed. 
 
     
     
       7. The engine rotational speed control apparatus as recited in  claim 6 , wherein
 the fuel amount comparing section is further configured to determine if a change from the rotational speed suppression operating point to the fuel economy consumption operating point is in progress, and to use an engine rotational speed obtained by adding a prescribed rotational speed to a current target engine rotational speed instead of using the current target engine rotational speed when the operating point change determining device determines that a change from the rotational speed suppression operating point to the fuel economy consumption operating point is in progress. 
 
     
     
       8. The engine rotational speed control apparatus as recited in  claim 4 , wherein
 the engine rotational speed decrease amount is set in accordance with an output rotational speed of the continuously variable transmission such that as the output rotational speed of the continuously variable transmission becomes slower, the engine rotational speed decrease amount becomes smaller. 
 
     
     
       9. A vehicle comprising:
 an engine; 
 a continuously variable transmission operatively coupled to the engine; and 
 a control apparatus having a configuration that selectively controls a gear ratio of the continuously variable transmission and an engine control parameter of the engine such that the engine operates at an operating point that achieves a target drive force based on a vehicle speed and an accelerator position, with the operating point of the control apparatus being based on a combination of an engine rotational speed and an engine load lying on a predetermined operation curve in an operation region of the engine that is defined based on the engine rotational speed and the engine load, 
 the configuration of the control apparatus being further configured such that when the target drive force increases to an increased target drive force while the engine is operating at the operating point on the predetermined operation curve, the gear ratio of the continuously variable transmission and the engine control parameter are controlled to operate the engine at an alternate operating point that achieves the increased target drive force with a lower engine rotational speed and a higher engine load than a standard operating point that lies on the predetermined operation curve and corresponds to the increased target drive force, and afterwards the gear ratio of the continuously variable transmission and the engine control parameter are controlled such that the engine operates at the standard operating point that lies on the predetermined operation curve and corresponds to the increased target drive force.